1. Field of the Invention
The present invention relates to an air-conditioning apparatus for vehicle use, which conditions air within a passenger compartment of, for example, an electric automobile not having engine coolant water nor equipped with an air-cooled type internal combustion engine or the like.
2. Related Art
Japanese Patent Application Laid-open No. 4-151324 discloses an air-conditioning apparatus for vehicle use in which a passenger compartment cannot use a heater that relies upon exhaust heat from engine coolant water, as, for example, is true in the case of electric automobiles. This document teaches a first heat exchanger and a second heat exchanger installed in a refrigeration cycle within a duct for sending air to a passenger compartment of an electric automobile. Furthermore, this document switches the direction of refrigerant flow within the refrigeration cycle by means of valves or the like so as to cause each heat exchanger to function as an evaporator during a cooling mode and as a condenser during a heat pump heater mode.
However, because this document teaches using a structure whereby first and second heat exchangers of a refrigeration cycle are disposed within a duct, an existing heater unit provided with a conventional hot-water heater core could not be used. For this reason, it is necessary to provide an air-conditioning unit provided with first and second heat exchangers, thus leading to the problem of high cost of the system.
Additionally, according to known technology, water capacity declines extremely when ambient air temperature drops to 0.degree. C. or less during the heat pump heater mode, which causes the first and second heat exchangers within the duct to function as condensers. Particularly in a cold-climate region (a region where the ambient air temperature drops to -10.degree. C. to -30.degree. C. or less), with such a heat pump heater, the problem existed that the heater had insufficient capacity. Accordingly, because a heat pump heater has a diminished capacity in a cold-climate region, performing hot-water heating utilizing a combustion type heater as a heat source for heater use in cold-climate regions may be considered.
However, according to the document noted above, because a hot-water cycle provided with hot-water heater devices of a hot-water heater core, water pump, hot-water piping, and the like is not mounted in an electric automobile, a hot-water heater device must be added in order to function as a combustion type heater, and assembling such a fixture within an air-conditioning unit posed problems of extreme difficulty and resulting high cost.
Moreover, even if the cooling of vehicle-mounted electrical devices of, for example, a motor for travel use, an inverter for travel use, etc., of an electric automobile is performed with water cooling, the exhaust heat of this vehicle-mounted electrical device is not employed for heating the air within the passenger Compartment, and so energy is not effectively and sufficiently utilized when the overall energy consumption and utilization of the vehicle is considered.